Hitherto, plural open flow switches OFS1 of the OFS5 have been employed for communication of packets between plural clients C1 to C4 and a server S1. When such communication is performed, communication of the packets is not possible when, for example, an obstruction has occurred on a link between switch OFS4 and OFS5. In such cases, there is a need to find out on which link the obstruction has occurred. Therefore, passive monitors have hitherto been employed to collate packets and identify obstruction locations.
However, depending on the placement location of the passive monitor, sometimes analysis of an obstruction is not possible. Namely, as illustrated in FIG. 32A, when a passive monitor is provided between the server S1 and the switch OFS5, the passive monitor is able to receive packets from the transfer path of all of the switches OFS. The passive monitor can accordingly determine an obstruction between switch OFS4 and switch OSF5. However, as illustrated in FIG. 32B, a case may be considered in which the passive monitor is provided between the client C1 and the switch OFS1. When an obstruction occurs between the switch OFS4 and the switch OFS5, the passive monitor provided between the client C1 and the switch OFS1 cannot receive packets that have passed through between the switch OSF4 and the switch OSF5. The obstruction location can therefore not be identified in such a case.
The placement location of a passive monitor is therefore a location that enables obstruction analysis.